If he's very serious about the changes he's proposing he will get involved in a program of recovery, get himself into counseling and his actions while still being apart from you can tell you whether he's invested in changing.
I always found the most difficult stage w AH to be when he'd go from angry/accusatory to apologetic and full of promises. I so badly wanted to believe his claims he wanted to make things better that I got sucked back in time and time again. The result? His abuse got worse, he didn't keep a single promise and it for harder to leave.
If he doesn't want the kids raised in a home w stress then he needs to look at himself and focus on his issues. Marriage counseling w an active addict is not a good idea. It will turn rapidly into him convincing you and the therapist this is a marriage problem vs an abuse problem.
You can tell him you'll give it a chance but that you'll do it while separated. His actions, not words are what count.
He hasn't gotten his way by bullying or playing the poor me card so now the promises come bc that's the next tactic in the toolkit of manipulators.
Please stay strong. You are worth it!